The studies detailed below will address the role of surface receptor molecules, specifically those of the opioid receptor family and the receptor for the cytokine interleukin-8 (IL-8), in the function of immune competent cell populations in the brain. These studies will examine the activity of brain macrophages and microglia both in the developmental period and in response to injury using an animal model of neuronal injury. Initially, brain and non-central nervous system (CNS) immune cell populations will be isolated from rats at various points during development, maintained in culture and examined for expression of sequences coding for the production of the receptors of interest by in situ hybridization and RNase protection analysis. Immune cells will also be activated by exposure to conditioned media from visual cortex ablation studies and examined in the same manner to document expression changes in the activated state. Visual cortex ablation studies will be performed in animals of different ages and brain macrophages and microglia in the dorsal lateral geniculate nucleus (dLGN) examined by these molecular techniques and immunohistochemistry using receptor specific antibodies in order to demonstrate expression patterns and changes in vivo. Finally, intracerebral injections of IL-8 and systemic administration of opioid receptor blockers will be used to assess directly the role of the these two systems in mediating chemotaxis by immune competent cells. Opioid receptor blockers will also be administered to animals receiving visual cortex ablation to examine the role of the opioid receptor system in the brain response to traumatic injury.